Halogen-containing polymers or plastics or molded articles produced therefrom tend to undergo substantial changes during their production process and under environmental influences. For example, they tend to decompose and degrade under the influence of heat and/or light. The degradation of such halogen-containing polymers, in particular PVC, produces halogenic acid (in case of PVC hydrochloric acid), which is eliminated from the polymer strands, resulting in a discolored, unsaturated plastic having chromophoric polyene sequences.
To avoid these undesirable changes, it is common practice in the art to add stabilizers to these polymers that at least partially prevent decomposition and/or discoloration first during the production process and then later on during the lifetime of the product. In the past, toxic heavy metal-containing compounds, such as lead, barium or cadmium containing compounds, have been used as stabilizers. However, due to the toxicity and environmental concerns, in the recent years, attempts have been made to find alternative stabilizers. Today a growing number of heavy metal-free stabilizer compositions is available, including among others, hydrotalcites, perchlorates, alkaline earth metal oxides, hydroxides and carboxylates, etc. Other known stabilizers include nitrogen-containing compounds, such as aminouracils and isocyanurates.
Photoblueing, i.e. a light-induced color shift to blueish colors, occurs when halogen-containing polymer products, in particular PVC products, are irradiated by sunlight in the first hours after production. This phenomenon is an issue for PVC window profiles, because it is desirable that the tone should fit to profiles from different batches when confected. The photoblueing effect, which is manifested by a decrease in the b value (of the Lab color space), can be influenced by different components in the polymer composition. One example of a compound that influences the photoblueing behaviour is the white pigment titanium dioxide. Interestingly, the modification of titanium dioxide, i.e. whether it is present in the rutile or anatase modification, also influences the photoblueing effect. In addition, the type of stabilizer used to stabilize the halogen-containing polymer can influence photoblueing behaviour.
In contrast, the type of polymer, in particular the PVC type, commonly used fillers and modifiers, and the nitrogen and oxygen concentrations in the environment, do not significantly affect photoblueing behaviour.
Although high amounts of antioxidants or protection of the polymer products from light, in particular sunlight, can decrease or prevent photoblueing, it would be desirable to have compounds available that can prevent or compensate for the color change. Accordingly, there is need in the art for compositions and methods that can reduce the photoblueing effect.